PROJECT SUMMARY: Neuronal networks must function reliably throughout life in spite of molecular turn- over and developmental and environmental changes. This is most evident for pattern-generating neural circuits underlying vital behaviors such as breathing. Activity-dependent homeostatic regulation (ADHR)of network properties supports stable network function through a feedback loop between a circuit's electrical activity and the underlying cellular and synaptic properties. Intracellular calcium levels play an important role in this feedback loop because they act as sensors of electrical activity and are involved in intracellular signaling, but the pathways underlying ADHR are not understood. This grant will use computational brute force to examine millions of different models of ADHR,with the aim of identifying regulatory pathway structures that support stable network function and can restore it after perturbations. Analyzing the common properties of successful regulation models will identify key features of ADHR pathways and reveal how neuronal networks can maintain stable function. The proposed researchwill use the lobster pyloric pattern- generating circuit as an established model system in which ADHR has been demonstrated at the cellular and network levels. Simulations will proceed in three steps: 1) identifying calcium-based activity sensors that distinguish functional from non-functional network activity, 2) determining how these sensors feed back onto neuronal properties to achieve homeostasis at the cellular level, and 3) testing regulation mechanisms that are successful at the cellular level for their ability to support homeostasis at the network level. Because little is know about ADHR of synaptic properties in pattern-generating circuits, experiments will determine whether and how synapses in the pyloric circuit are homeostatically regulated, and results from these experiments will inform the final network level simulations. RELEVANCE:Maintaining stable neural network function, especially in pattern-generating circuits, is of vital importance for any animal, including humans. Homeostatic regulation failure can lead to disfunctional network outputs including silence or seizure-like activity, and has been implicated in epilepsy and other seizure disorders and in the response of brain tissue to trauma or hypoxia. This grant will contribute to a better understanding of homeostatic regulation processes in neural circuits and will thus lay the groundwork for potential treatments of these disorders.